The invention relates to a process for the production of a valve, in particular a charge cycle valve of an internal-combustion engine.
U.S. Pat. No. 2,316,488 discloses a valve composed of two separately produced parts of different material for an internal-combustion engine. The valve has a cast hollow shank of high tensile strength, filled with coolant, as well as a highly heat resistant valve disk, which forms the valve base and valve back extending beyond the valve seat and reaching as far as the point of connection of the valve disk with the widening valve shank. The valve shank and valve disk are welded to each other at this point of connection. The purpose of this two-part construction of the valve with a cast valve shank is to save on highly heat resistant material, which is also difficult to work, by using it only for the highly stressed valve disk itself. In the case of such a valve, although the valve shank can be cast in a simple way, it is necessary subsequently to further machine the valve shank to improve the surface quality. In this machine operation, material is removed from the shank surface, which requires that the wall of the shank be of a certain sufficient thickness. By prescribing this minimum wall thickness, the interior space which can be filled with coolant is inevitably smaller and the weight of the valve shank increases.
The object of the present invention is therefore to produce a valve of the generic type in such a way that a solid and yet lightweight valve which is provided with a large interior volume can be made in a simple production operation.
This object is achieved according to the invention by cold forming of a tubular starting material. That is, the tubular starting material is reduced at a temperature which lies below the recrystallization temperature of the material, at its one end from its original diameter to the desired valve shank diameter, for example by round kneading with an inserted mandrel corresponding to the desired internal cross-section of the valve shank. In the same operation, the transitional region between unworked, tubular starting material and reduced valve shank is shaped by means of the kneading operation with suitable tools as a shank section widening in the form of an arc. This finally formed valve shank is subsequently severed from the tubular starting material at a point corresponding to the diameter of the connection between the valve disk and valve shank. Thereafter, the valve shank is welded to the valve disk, produced from a highly heat resistant material in its own working operation, and, after any appropriate filling of the valve with a coolant, is closed at the top shank end, which was previously open. The expensive, highly heat resistant material which is difficult to work is used only for the production of the highly stressed valve disk, whereas a cheaper starting material which is easier to work may be employed for producing the less stressed valve shank. Within the scope of the invention, the internal cross-section can be maintained exactly by means of an inserted mandrel. In addition, a shank surface of high quality with low peak-to-valley height is formed, which simplifies the subsequent finishing of the valve shank.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.